This invention relates to a multilayer film suitable for use as an anti-reflective coating on a glass substrate. More particularly, this invention relates to a multilayer film stack with a first layer of a metal oxide, or doped metal oxide having a high refractive index, combined with a second layer of a metal oxide having a low refractive index. The thickness of the first layer is greater than conventional 1/4 wavelength anti-reflective coatings. The thickness of the second layer is less than wavelength coatings. The multilayer film is generally applied pyrolytically onto a glass substrate in a float glass production process.
Coatings on glass are commonly utilized to provide specific energy attenuation and light transmittance properties. Additionally, coatings are designed to reduce reflections from interfaces between individual coating layers and the glass when a plurality of coatings are applied onto a glass substrate. The coated articles are often utilized singularly, or in combination with other coated articles, to form a glazing.
The attributes of the resulting coated glass substrate are dependent upon the specific coatings applied to the glass substrate. The coating compositions and thicknesses impart energy absorption and light transmittance properties within the coated article while also affecting the spectral properties. Desired attributes may be obtainable by adjusting the compositions or thicknesses of the coating layer or layers. However, adjustments to enhance a specific property can adversely impact other transmittance or spectral properties of the coated glass article. Obtaining desired spectral properties is often difficult when trying to combine specific energy absorption and light transmittance properties in a coated glass article.
Anti-reflective coatings on glass are utilized to reduce the surface reflection of optical components and to reduce the reflectance of an interface between optical media with different refractive indices. The reduction of visible reflection is achieved by the principle of optical interference. When light impinges on the air-film, film-film, and film-glass interfaces, a portion of the beam is reflected at each interface. By proper choice of thin film materials and thicknesses, the individual reflected light beams can destructively interfere, thereby reducing the observed visual reflectance.
Conventional two layer anti-reflective films generally follow a standard design formula to optimize the reduction of visible light from the interfaces of the coated glass substrate. The standard design parameters suggest the use of a two layer coating, of both high and low indices, with each coating having a thickness determined by l/(4*n), where l is a design wavelength in the visible region, and n is the refractive index of the coating. While the coated glass substrates produced in accordance with the standard design have an effect upon the reflective properties of the glass, the individual layers require thicknesses that are often difficult to produce on-line pyrolytically on a moving ribbon of glass.
It would be advantageous to reduce reflection properties of a coated glass substrate over conventional anti-reflective films.
It would be a further advantage to provide an anti-reflective film that may be applied pyrolytically onto a glass substrate. A pyrolytic film enables the deposition of the film on-line, for example, in a float glass production process.